A general process starting from the production of conventional plastic lenses for spectacles until the attachment of the plastic lenses for spectacles to a spectacle frame will be briefly described below.
First, a plastic lens material is poured into a mold cavity and cured to form lenses with a predetermined shape by a known technique such as cast molding or injection molding. The formed lenses may be classified into those of a lens blank type (including semi-finished lenses) which has an optically unfinished surface on at least one side thereof, and those of a finished lens type which has optically finished surfaces on both sides thereof.
In the case of finished lenses, after various coatings such as hard coating, antireflection coating, water-repellent coating, antifog coating, antifouling coating and mirror coating have been applied to the lens surfaces including both the optical surfaces, the lenses are subjected to edging according to the order of the customer and is, if necessary, subjected to machining for attachment to a frame. Then, the machined lenses are attached to a spectacle frame, whereby a pair of spectacles is completed.
In the case of lens blanks, the optically unfinished optical surfaces are cut and polished into optically finished surfaces according to the order of the customer to form finished lenses. The subsequent process is the same as that for finished lenses; i.e. after various coatings have been applied to the lens surfaces, the lenses are subjected to edging and, if necessary, to machining for attachment to a frame and the machined lenses are then attached to a spectacle frame, whereby a pair of spectacles are completed.
The term “edging” as used herein is intended to refer to machining of an edge of the lens for shaping the lens to fit a lens rim of a given spectacle frame into which the lens is intended to be attached or to conform to a designated lens shape, and also refer to machining of the edge of the lens so that the lens has a desired peripheral edge shape (or example, to form a peripheral edge with a bevel, a flat surface or a groove or to chamfer the corners where the optical surfaces meet the peripheral edge).
The term “machining for attachment to a frame” as used herein is intended to refer to a machining operation to form holes, grooves or the like in an optical surface near the edge of the edged lens or in the peripheral edge of the edged lens when the lens is intended to be attached to a spectacle frame, such as a rimless frame, which does not have rims that surround lenses. The holes and grooves are used in attaching the lenses to the frame (endpieces or a bridge).
Edging and the machining for attachment to a frame are herein collectively referred to as “lens machining.”
The term “bevel” as one example of the peripheral edge shapes is intended to refer to a ridge with a V-shaped protrusion which has a V-shaped cross-section and is formed circumferentially along the peripheral edge of the lens and is used when the lens is attached to a full-rim frame, for example.
The term “groove” as one example of the peripheral edge shapes is intended to refer to a groove used, for example, when the lens is attached to a mount for a semi-rimless spectacles (half-rim frame) or a spectacle frame having a wire rim or a thin plate rim. The groove is configured to be in fitting engagement with a member for supporting the lens, such as a band, e.g., a nylon yarn, a T-slot, a wire, a thin plate member or the like and is formed circumferentially along a part or entire peripheral edge of the lens. Such a groove generally has a cross-sectional shape having a width of about 0.5 to 1 mm and a depth of about 0.3 to 0.6 mm and a bottom with a semi-circular, V-shaped, rectangular or inverted trapezoidal shape.
The term “flat” as one example of the peripheral edge shapes is intended to refer to a peripheral edge shape of a lens which does not have any projections or recesses and is flat in cross-section and which is employed when the lens is intended to be fitted to a spectacle frame, such as a rimless frame, which does not have rims that surround lenses.
In some cases, the entire production process described above may be carried out in a lens maker and the completed spectacles may be delivered to an optician's shop or the customer. In other cases, the spectacles lenses which have been provided with various coatings but have not edged yet may be delivered from the lens maker to the optician's shop and edging and subsequent processes are carried out in the optician's shop. In still other cases, spectacles lenses which have been provided with various coatings and subjected to edging may be delivered from the lens maker to the optician's shop and the processes subsequent to the edging are carried out in the optician's shop.
FIG. 1 illustrates an example of a conventional edged plastic lens for spectacles which has been cut to fit a rimless frame generally called two-point or three-piece frame. In FIG. 1, a lens 10 is formed by edging a lens, which has optically finished optical surfaces on both sides thereof and is provided with various coatings including a hard coating, into a designated lens shape. Namely, the lens 10 has optical surfaces dens front surface 11 and lens back surface 12) with various coating including a hard coating thereon and a peripheral edge 13 where the lens substrate material is exposed as a result of the edging. The peripheral edge 13 has a dull finish in some cases and has a glossy finish obtained by polishing in other cases. The lens 10 has screw holes 14a and 14b (generally having a diameter of about 1.6 to 2.0 mm) for screws with a diameter of about 1.4 mm drilled at positions near its right and left peripheral portions and extending through the lens front and back surfaces so that lens-holding portions such as a bridge and an endpiece can be secured using the holes 14a and 14b and the screws with the lens front and back surfaces sandwiched therebetween.
In the embodiment shown FIG. 1, holes are formed through the optical surfaces by the machining for attachment to a frame. As other embodiments of the machining for attachment to a frame, there may be mentioned a hole extending from the peripheral edge of the lens into the inside of the lens (Patent Document 5 and Patent Document 7), a groove in the peripheral edge of the lens (Patent Document 6) and a groove in an optical surface of the lens (FIG. 14 of Patent Document 7).
The lens material used for plastic lenses for spectacles is discolored after shaping by the effect of light (Ultraviolet radiation (UV), in particular) from the ambient environment. In recent years, lenses having a high sulfur content (40% or higher, for example) and lenses containing a component having an aromatic ring are provided in response to increasing demand for a high refractive index. However, the problem is that these lenses are inferior in light stability as compared with conventional lenses. Thus, plastic lenses for spectacles are usually provided with UV absorbing capability. For example, the light stability of plastic lenses are improved by mixing an UV absorbing agent in a plastic lens monomer and polymerizing the monomer (Patent Documents 1 and 2), by immersing the plastic lenses in an aqueous solution containing an UV absorbing agent dispersed therein (Patent Document 3), or by applying a substance that absorbs and/or scatters UV to surfaces of the plastic lenses (Patent Document 4).
By imparting UV absorbing capability to plastic lenses as described above, discoloration of the lenses can be prevented to a large extent. Also, while the portions of lenses close to their surfaces are more likely to be discolored than their interior portions, the surfaces of lenses before edging are prevented from being discolored, since the surfaces of the lenses are provided with coatings such as a hard coatings and an antireflection coating as described before and since a component contained in the coatings such as Ti serves to reflect or absorb UV.
However, there is no coating such as a hard coating or an antireflection coating on a peripheral edge of a lens which has been subjected to edging or on a surface which has been subjected to machining for attachment to a frame (In the present specification, such a surface may be occasionally referred to simply as “machined surface for attachment to a frame.” Further, the machined surface for attachment to a frame (such as the above-described interior surfaces of the screw holes 14a and 14b) and the peripheral edge of an lens which has been subjected to edging (peripheral surface formed by edging) may be occasionally referred to collectively as “machined lens surface”). Thus, the bare substrate material is exposed at the machined lens surfaces. Therefore, the portions of the lens close to these surfaces are more likely to be discolored than its interior portion and the lens surfaces (generally lens optical surfaces) which are coated with a hard coating or an antireflection coating.    Patent Document 1: JP S58-122501A    Patent Document 2: JP 2001-91906A    Patent Document 3: JP 2001-91908A    Patent Document 4: JP H09-265059A    Patent Document 5: JP H07-230062A    Patent Document 6: JP 2002-14303A    Patent Document 7: WO2004/107021A